1. Field of the Invention
The present invention relates generally to a fluid-filled engine mount capable of exhibiting vibration damping effect or action based on resonance or flow action of non-compressible fluid sealed therein. More specifically, the present invention is concerned with such a fluid-filled engine mount of novel structure that is capable of providing excellent vibration damping or isolating effect against input vibration over a wide frequency band by automatically controlling its damping characteristics in accordance with fluctuation of vibrations to be damped, without needing complicated control means such as switch valves and control devices.
2. Description of the Related Art
Vibrations (including noises induced by the vibrations) in a body or various components of an automotive vehicle often become a major problem, and, in order to isolate such vibrations, an engine mount for suppressing the vibration transmission from a power unit, which is one of the sources of vibration, to the body has been conventionally employed.
As one type of such vibration damping devices, known is a fluid-filled engine mount having a non-compressible fluid sealed within a fluid chamber thereof and which provides passive vibration damping effect by utilizing resonance of the non-compressible fluid that is forced to flow therein upon the input of vibration. A known example of such a fluid-filled engine mount is disclosed in Citation 1 listed below. However, this type of engine mount suffers from a problem that the damping effect is effective only to the narrow frequency range to which the orifice passage is tuned.
Typically, automotive vehicles are subjected to vibrations whose frequencies are changed depending upon driving condition thereof. When driving, a vehicle tends to suffer from driving booming noises or other high frequency and small-amplitude vibrations, or engine shapes or other low frequency and large-amplitude vibrations. When idling, the vehicle tends to suffer from idling vibrations or other medium frequency and medium amplitude vibrations. That is, vibrations excited in automotive vehicles will be over a wide frequency range.
In order to provide different damping performances depending on driving conditions, the present assignee has disclosed in the following Citation 2, a switch-control type fluid-filled engine mount whose damping characteristics can be switched among different values under control. Namely, the disclosed engine mount incorporates two different orifice passages that are alternately affected by changing air pressure applied thereto, whereby the engine mount can exhibit different damping effects with respect to different frequency ranges to which the two orifice passage is tuned on the basis of resonance of the fluid flowing through the respective orifice passages.
However, the switch control type fluid-filled engine mount must be assembled, in order to control applied air pressure, with switch valves, drive means for driving the switch valves, control means for controlling the drive means, and various of sensors for sensing signals required in the control means. Therefore, the number of components will increase, and the construction of the device will become extremely complex, making the assembly procedure become troublesome, and increasing the manufacturing costs.
[Citation 1] JP-A-57-009340
[Citation 2] JP-A-06-089803